The present invention is directed to improvements in forming molded polymeric articles, and includes a method for making microreplicated articles and a method of making molds for such articles for use in injection or insert molding processes. The present invention also is directed to improved surface topography features for polymeric articles.
Minnesota Mining and Manufacturing Company has recently introduced a friction control material for use on glove and handle wrap applications which facilitates high slip resistance in the direction of shear, in wet or dry conditions. This material, known as GREPTILE™ gripping material is commercially available in sheet and strip form. The material has a surface defined by an array of elastomeric uniformly shaped upstanding stems which are highly flexible. When a normal force is applied to the stem array surface, the stems deform and bend over, thereby increasing the effective surface area of the gripping material relative to the applied shear forces. The material thus presents an aggressive friction control surface. When used with a like material in an opposed relation, the stems of the two materials interengage, thereby presenting even more surface area to each other for relative frictional interface. The stems do not interlock, however, so virtually zero peel force is required to separate the two opposed stem arrays. This material is more fully disclosed in U.S. Pat. No. 6,610,382 (which is incorporated by reference herein), commonly owned by the applicant herein, 3M Innovative Properties Company.
Known stem-web containing polymeric articles are often formed by molding techniques. When the desired article includes intricate or numerous topography features, the mold must necessarily include such intricate and numerous topography features, in mirror image. Creating such intricate features on molds has heretofore been a relatively expensive proposition. For instance, if the mold is to include microreplicated features such as generally cylindrical headless stem elements, the mold must include a hole or channel for each stem to form therein, and those holes must thus be individually drilled in the mold material. Attempts to use mold segment replication have been tried, but such an approach is limited by molding and pattern materials that will suffice for such replication purposes for a microreplicated surface, and still result in relatively expensive mold production techniques.